Comparison and optimization of the transmission performances of various advanced modulation formats in high bit rate systems

Abstract

As is well known, chromatic dispersion (CD) and nonlinear effect such as self-phase modulation (SPM), cross-phase-modulation (XPM), and four-wave-mixing (FWM), as well as their impairments interaction with each other are recognized as a limiting impairment for a high bit rates optical systems. With the advent of the 40 Gb/s, it is necessary to study transmission performance, which clearly depends on the modulation format and the system design. A numerical comparison of non-return-to-zero (NRZ), return-to-zero (RZ) and differential phase shift keying (DPSK) formats is made at a bit rate of 40 Gbit/s for single-channel and WDM systems with different compensation method in attempt to find the optimum modulation format. The transmitter under consideration used a 1.5 um DFB-laser externally modulated by a MZM modulator with modulation format (NRZ, RZ, DPSK), 64 PRBS data. At the receiver end an optical filtering using gaussian, fabry-perot and rectangular filter is used. Between the compensation method the symmetrical design leaves the best results in comparison to pre- and post-compensation. The impact of SPM can be reduced considerably by the symmetrical design. NRZ shows a best toleranz again chromatic dispersion and DPSK a best toleranz to Nonlinearity.